Pachychelium tropicalis, Lowry & Stoddart, 2012

Lowry, J. K. & Stoddart, H. E., 2012, The Pachynidae fam. nov. (Crustacea: Amphipoda: Lysianassoidea) 3246, Zootaxa 3246 (1), pp. 1-69 : 35

Pachychelium tropicalis sp. nov.

( Figs 23–25 )

Type material. HOLOTYPE, sex not known, 2.7 mm, AM P.46674, off Flynn Reef , Queensland, Australia, 16°37.81'S 146°23.08'E, 1000 m, trap sample with sediment, 5.2° C, J.K. Lowry, P. Freewater & W. Vader, 6–7 June 1993, RV Sunbird, SEAS Project, stn QLD-930.

Type locality. Off Flynn Reef , Queensland, Australia, 16°37.81'S 146°23.08'E, 1000 m depth .

Etymology. The specific name reflects the unusual geographic position of this species.

Diagnostic description. Head lateral cephalic lobe large, narrowly rounded; ventral margin curved. Antenna 1 peduncular article 1 without posterodistal spine; accessory flagellum 2-articulate, article 1 long; flagellum with weak 1-field callynophore in specimen of unknown sex. Mandible lacinia mobilis absent; lamina dentata absent; accessory setal row absent; molar absent; palp attached distally; palp article 2 broad, shorter than article 3; article 3 with subparallel margins. Maxilla 1 outer plate with 6 setal-teeth in 4/2 arrangement, one outer row setal-tooth with medial cusps; palp absent. Maxilliped inner plate absent; outer plate medium size; palp 3-articulate (article 4 absent), article 3 length 3.2 × breadth. Gnathopod 1 subchelate; ischium smaller than propodus, not swollen posteroproximally; carpus extremely compressed; propodus length about 2 × breadth, posterior margin absent, palm without produced posterodistal corner, without robust seta. Gnathopod 2 palm minute, obtuse. Pereonite 4 without dorsal spines. Pereonite 5 without dorsal spines. Pereopod 5 merus without posteroproximal shoulder. Pereopod 6 basis with posteroventral lobe weakly produced; merus longer than broad, without posteroproximal shoulder. Pereopod 7 basis subovate with posterior margin smooth; merus, length of anterior margin 2.4 × proximal breadth. Epimeron 3 posterior margin without projections, posteroventral corner broadly rounded. Uropod 3 biramous, inner ramus just reaching base of article 2 of outer ramus. Telson longer than broad, entire.

Remarks. Neither P. tropicalis nor P. davidis has a defining corner on the propodus of gnathopod 1. They differ in the length of the mandibular palp article 2 (shorter than article 3 in P. tropicalis , subequal in P. davidis ); the shape of mandibular palp article 3 (parallel margins in P. tropicalis ; tapering distally in P. davidis ); and the basis of pereopod 5 (subquadrate in shape in P. davidis ; subovate in P. tropicalis ). Pachychelium tropicalis is the only species of the genus known to occur in the tropics and in the southern hemisphere.

Distribution. North-eastern Australia, Coral Sea, western South Pacific Ocean; 1000 m depth.

Figures

FIGURE 23. Pachychelium tropicalis sp. nov. Holotype, 2.7 mm, AM P.46674, off Flynn Reef, Queensland, Australia.

FIGURE 24. Pachychelium tropicalis sp. nov. Holotype, 2.7 mm, AM P.46674, off Flynn Reef, Queensland, Australia. Scales for A1, 2 represent 0.1 mm, remainder represent 0.05 mm.

FIGURE 25. Pachychelium tropicalis sp. nov. Holotype, 2.7 mm, AM P.46674, off Flynn Reef, Queensland, Australia. Scales represent 0.1 mm.